Downspout Calculator
Enter your size to get downspout quantity, plus an estimated cost. Waste is included and prices are editable.
Material needed
Estimated cost
How to calculate downspout
Downspout sold by the foot. Enter downspout length to get feet needed.
Formula: quantity = length × 1 × (1 + waste %) = 20 × 1 × 1.10 = 22 ft.
Worked example
Example: 20 ft long. Quantity: 22 ft, about $220 at $10 per ft.
Tips
Measure the full area, then subtract large openings if you want an exact count. Order a little extra for cuts and breakage, and confirm quantities with your supplier before you buy.
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Frequently asked questions
How much downspout do I need?
Example: 20 ft long. Quantity: 22 ft, about $220 at $10 per ft.
How much waste should I add?
Add 10% for straight areas and 15% for areas with many cuts, corners and openings.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.